1. Field of the Invention
The present invention relates to an apparatus for producing silicon nanocrystals based on inductively coupled plasma (ICP) and, more particularly, to an apparatus for producing silicon nanocrystals, which can minimize plasma diffusion by finely adjusting a plasma region created by an ICP coil.
2. Description of the Related Art
Recently, silicon nanocrystals have been generally used as photoelectric conversion/photo conversion materials such as solar cells or light emitting devices (LEDs). Silicon is an environmentally friendly material, abundant in the Earth's crust and is utilized for various applications in the field of electronic materials. Although silicon exhibits very undesirable optical characteristics in a bulk sate, silicon nanocrystals exhibit highly efficient optical characteristics.
A method of producing silicon nanocrystals can generally be classified into solid state reaction, liquid state reaction, and vapor state reaction.
In the solid state reaction, a thin film of SiO2, Si3N4, SiC or the like containing an excess of Si is first formed and are then subjected to heat treatment at high temperatures for condensation of silicon to form silicon nanocrystals in a SiO2, Si3N4 or SiC matrix. As such, the solid state reaction requires the heat treatment at high temperatures to form the silicon nanocrystals and incurs very high manufacturing costs due to expensive deposition equipment.
In the liquid state reaction, silicon nanocrystals are prepared through chemical reaction of silicon compounds, such as a high temperature supercritical method, reduction of silicon halide, and the like. The liquid state reaction has severe difficulty in controlling the particle size of the nanocrystals and incurs low quality in terms of crystallinity and the like.
In the vapor state reaction, silicon nanocrystals are prepared by passing a silane compound gas through a high energy region such as laser or plasma. Since the vapor state reaction allows the silicon nanocrystals to be formed not only in a matrix as in the solid state reaction but also without the matrix, the vapor state reaction produces high purity silicon nanocrystals and permits easier control of the particle size than the other methods.
A high energy source for the vapor state reaction is generally obtained from laser or thermal plasma. With such an energy source, however, the silicon nanocrystals are to aggregated due to high calorific heat, thereby forming secondary particles having a size of several micrometers (μm).
To solve such problems, non-thermal plasma such as inductively coupled plasma (ICP) has recently been used to prevent aggregation of the silicon nanocrystals.
A conventional apparatus for producing silicon nanocrystals based on ICP includes a reactor and an ICP coil wound around the reactor, and is configured to simultaneously supply a primary gas for forming silicon nanocrystals and a secondary gas for surface reaction of the silicon nanocrystals to the reactor.
However, the conventional ICP-based apparatus has a wide plasma reaction area caused by plasma diffusion inside the reactor. As a result, it becomes difficult to control the particle size of the silicon nanocrystals. The plasma diffusion also causes a wide reaction area of the secondary gas and extends reaction time, thereby deteriorating quality of the silicon nanocrystals.
Therefore, there is a need for an apparatus for producing silicon nanocrystals, which can minimize plasma diffusion inside the reactor in production of the silicon nanocrystals using ICP to improve the particle size characteristics and quality of the silicon nanocrystals.